No overload for 'textBox1_TextChanged_1' matches delegate 'System.Threading.TimerCallback

Question

I want to use System.Threading.Timer so that I can use this timer to call method "CreateThread" which is as follows.

public void CreateThread()
    {
        th1 = new Thread(ChangeLabel);
        th1.Start();
    }

I am getting error at line:

public void textBox1_TextChanged_1(object sender, EventArgs e)
    {
       TimerCallback tcb = new TimerCallback(CreateThread); //This line is showing error
    }

Can anybody please explain what is the problem?

Answer 1

TimerCallback expects a state property in the delegate:

public void CreateThread(object state)
    {
        th1 = new Thread(ChangeLabel);
        th1.Start();
    }

MSDN:

public delegate void TimerCallback(
    Object state
)

Answer 2

The problem is your method signature doesn't match with the TimerCallback delegate.It takes an object as parameter, but your method takes nothing.

Answer 3

If you look at the MSDN Documentation for the TimerCallback delegate, you will see that it has a signature of void TimerCallback(object).

The method you want the timer to call needs the same signature so that it will compile.

Something like this would fix it:

public void CreateThread()
{
    CreateThread(null);
}

private void CreateThread(object state)
{
    th1 = new Thread(ChangeLabel);
    th1.Start();
}

This would allow any existing callers of CreateThread() to remain unchanged, whilst giving you a method with the correct signature to call the method.

Alternatively, you could do the following by using a lambda:

public void textBox1_TextChanged_1(object sender, EventArgs e)
{
   TimerCallback tcb = new TimerCallback(() => CreateThread());
}